The prior art dealing with catalytic cracking catalysts is voluminous with a basic goal being the preparation of modified zeolites for use as cracking catalysts. The following patents are representative of the prior art.
The use of conversion catalysts formed from a zeolite dispersed in a siliceous matrix has been disclosed in U.S. Pat. No. 3,140,249 and U.S. Pat. No. 3,352,796.
The use of blended matrix components, e.g., a catalyst comprising a zeolite, an inorganic oxide matrix and inert fines, which may be alpha alumina, is disclosed in U.S. Pat. No. 3,312,615. Catalysts comprising an amorphous silica-alumina, separately added alumina and a zeolite are disclosed in U.S. Pat. No. 3,542,670 and catalyst comprising a zeolite, an amorphous hydrous alumina and alumina monohydrate are disclosed in U.S. Pat. No. 3,428,550.
It has been disclosed that the steam and thermal stability of zeolites can be improved by the use of zeolites having a low level of alkali metal content and a unit cell size less than about 24.45 Angstroms (See: U.S. Pat. Nos. 3,293,192 and Re. 28,629 (Reissue of U.S. Pat. No. 3,402,996)).
Further, it has been disclosed (U.S. Pat. No. 3,591,488) that the hydrogen or ammonium form of a zeolite may be treated with steam at a temperature ranging from about 800.degree. to about 1500.degree. F., and then subsequently cation exchanging the steam treated zeolite with cations which may be rare earth metal cations. The method increases the silica to alumina mole ratio of the zeolite crystal framework lattice and also crystal structure imperfections. U.S. Pat. No. 3,676,368 discloses a rare earth exchanged-hydrogen faujasite containing from 6 to 14 percent rare earth oxides. U.S. Pat. No. 3,957,623 discloses a rare earth exchanged zeolite having a total of 1 to 10 weight percent rare earth metal oxide. U.S. Pat. No. 3,607,043 discloses a process for preparing a zeolite having a rare earth content of 0.3 to 10 weight percent.
U.S. Pat. No. 4,036,739 discloses hydrothermally stable and ammonia stable Y zeolite in which a sodium Y zeolite is ion exchanged to partially exchange sodium ions for ammonium ions, followed by steam calcination and a further ion exchange with ammonium to reduce the final sodium oxide content to below 1 weight percent, followed by calcination of the reexchanged product, or according to U.S. Pat. No. 3,781,199, the second calcination may be conducted after the zeolite is admixed with a refractory oxide.
A catalyst for the formation of high octane gasoline products and its use in cracking processes is disclosed in copending U.S. Ser. No. 657482, 10-3-84, filed concurrently herewith and commonly assigned. The catalysts of such copending application employ specific LZ-210 zeolites and have a critical effective amount of rare earth cations and a low Na.sub.2 O content, respectively, of from greater than zero to less than 5 percent by weight rare earth and less than 1.2 weight percent Na.sub.2 O, such being based on the weight of the LZ-210 component in the catalyst.